Coffin Bone Fractures

Q. My horse has been diagnosed with a fractured coffin bone. What could have caused it, and what is the prognosis?

A. Fractures of the coffin bone or distal phalanx usually occur in the horse following some type of trauma, often from kicking, or a large force placed on the coffin bone (i.e., racing on hard tracks). However, they can occur from a penetrating object or as the result of a severe infection of the hoof that has extended into the coffin bone. In these cases, the bone fracture is secondary to the infection. Although coffin bone fractures are uncommon compared to other fractures that occur in the horse, they occur most commonly in Standardbred racehorses, Quarter Horses, and Thoroughbred racehorses, and also can occur in foals. Fractures of the coffin bone occur most commonly in the forelegs, regardless of the breed or use of the horse.

Horses which sustain coffin bone fractures are moderately to severely lame, but the lameness is somewhat dependent on the location of the fracture. Also, the horse might be only mildly lame on the day the fracture occurred and much worse the following day after the tissue around the fracture has become swollen. To determine if your horse has a coffin bone fracture, your veterinarian will need to perform diagnostic tests on your horse, including applying hoof testers and possibly nerve blocks. The hoof testers are used to apply pressure to the hoof and underlying coffin bone. A reaction to the hoof testers indicates pain in the hoof or coffin bone that can be the result of a hoof abscess, navicular syndrome, or a coffin bone fracture depending on the location of the sensitivity. The nerve blocks cause desensitization of a certain area on the horse's limb and determine where the lameness is localized in the leg (i.e., the hoof). Radiographs (X rays) then are needed to definitively identify a coffin bone fracture. However, multiple films at different angles might be needed to pinpoint the location of the fracture.

Sometimes the fracture is not easily seen using radiographs immediately after the fracture has occurred. In those instances, nuclear scintigraphy (a bone scan) can be used to determine if a fracture is present. In those cases, radiographs can be used for diagnosis in about two weeks, after the body has removed some of the bone from the fracture line, making the fracture more easily seen on a radiograph. At that point, radiographs can determine the exact location of the fracture in the bone and let your veterinarian know if the fracture involves the joint.

Coffin bone fractures can occur in seven different types and are characterized by where in the bone they occur and if they involve the coffin joint (distal interphalangeal joint). Fractures of the bone that involve the coffin joint have a poorer prognosis due to the risk of the development of arthritis in that joint, often called low ringbone (see The Horse, February 2000, page 101). Fractures not involving the coffin joint usually have a fairly good prognosis for the horse returning to soundness.

Treatment of coffin bone fractures usually involves stall rest and the application of a bar shoe with either multiple quarter clips or a forged rim and a full pad. The rim or clips help keep the hoof from expanding with each step and therefore help the hoof act as a natural cast. Most horses, although quite lame in the beginning, will become more comfortable within one month. Treatment with phenylbutazone (Bute) can help alleviate some of the pain associated with these fractures and encourage the horse to bear weight on the affected leg. In horses with severe lameness associated with the fracture, pain alleviation is imperative to prevent laminitis or breakdown in the opposite leg.

Simple fractures of the coffin bone often require several months of rest to heal completely. The bar shoe will need to remain in place during this time. Subsequent radiographs will be necessary to determine when the fracture is healed completely and when the horse can return to work.

Fractures of the coffin bone that extend into the coffin joint are more difficult to manage and might require surgery to speed healing and/or prevent career-ending arthritis of the coffin joint. Surgery is used to compress the fracture gap, thus lessening the gap that the body must heal. Surgery also is used to decrease any defects that might have occurred in the articular cartilage of the coffin joint as a result of the fracture. Large defects in the articular cartilage predispose the horse to the development of arthritis, so minimizing the defect is paramount to preventing arthritis, and ensuring that the horse remains sound.

Successful treatment of coffin bone fractures is dependent on a few factors, one of the most important being a quick diagnosis by your veterinarian. So, if your horse becomes lame, you should have your veterinarian examine him as soon as possible. The second factor is the availability of a farrier who can create good-quality shoes that will encourage the fracture to heal; and the third is the location of the fracture, which unfortunately no one can control.

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